On a site I am re-developing atm there are so many duplicate pages in Google that its going to be near impossible to try and catch them all with perm redirects.
What I thought of doing instead was to move the whole site onto a new URL (widgets.com -> widgets.co.uk) and then just do a perm redirect on the home page of the old domain to the home page of the new page so that the PR and backlinks are carried across.
Do you see any problems in me doing this?
One thing to point out is that widgets.co.uk currently has a perm redirect to widgets.com.
Launching a new domain carry many issues -- the so-called sandbox effect being a big one. Also going from a .com to a .co.uk for the tld carries geo-location implications.
Changing domains is fraught with challenges and potentially sever bumps in the road. Only do it if you really "must" I would say. Better if you do what you can to clean up the existing domain, or perhaps even redevelop there according to your new scheme. I also would not focus on 301 redirect for the whole solution -- where are those other urls coming from? Plug those holes first.